Free-piston internal-combustion engine



Oct-28, 1947. H. STEINER I I FREE PISTON INTERNAL-COQBUSTION BNG INE 3 Sheets-Sheet 1 Filed May 9, 1945 mvsu'ron HA'MS JTE/A/[R ATTORNEY:

Oct. 28, 1947. H. STEINER 2,429,943

FREE PISTON INT RNAL-comausuon ENGINE Filed lay 9, 1945 3 Sheets-Sheet 2 v INVENTOR Hfl/VS 67E/NER BY Qua-n.1, 0......-

ATTORNEYS Patented Oet. 28, 1947 FREE-PISTON INTERNAL-COMBUSTION ENGINE Hans Steiner, Winterthur, Switzerland, assignor ete Anonyme, Winterthur,

to Sulzer Freres, Soci Switzerland Application May 9, 1945, Serial No. 592,745 In Switzerland May 12, 1944 9 Claims. (01. 12346) combustion engine and has the purpose of enabling the frequency of the stroke to be varied, and in particular to be increased.

For free-piston internal combustion engines it is known to employ an energy storage cylinder or buffer for regulating the length and frequency of the stroke of the free pistons,-at each stroke a gas, for instance air, being compressed and again expanding when the free pistons have reached the outer dead centre. The ener y collected in the buffer cylinder by compression serves to equalise the rest of the energy acting upon the free piston in the opposite direction, In stationary service the quantity of energy acting upon the free piston in one stroke must be equal to that acting in the other stroke, as otherwise the length of the stroke would be continuously increased or decreased.

In the present invention it is now proposed that at least one free piston should have two or more energy storage cylinders which absorb energy in different strokes, energy being generated by the rise of pressure at least in the latter part of the stroke.

Three embodiments of the invention are shown diagrammatically in the drawings. 4

Fig. 1 shows the diagrams of the quantities o energy acting on the power piston, the compressor piston and the buffer piston.

Fig. 2 shows the distribution of the accelerating and retarding work done on the free piston.

Figs. 3-8 show three different types of buffer cylinder and the appertaining diagrams.

Figs. 9 and 1.0 show the two energy'storage cylinders of a free piston with the appertaining diagram.

Fig, 11 shows an embodiment in which one end of a compressorcylinder serves as an energy storage cylinder.

Fig. 12 shows a further execution with a common regulating device for the buffer cylinders of the two free-pistons.

In Fig. 1 the forces acting on the mass of the free-piston in a free piston engine are set ofi on the ordinates with the stroke as abscissa, the upper section showing the total force of the power piston, the middle section that of the compressor piston and the lower section that of a buffer piston which absorbs energy during the outward stroke. Accordingly the area 01 represents the a to be equal to the The work done in compressing the combustion air in the combustion cylinder is represented by the area 0. This must again be equal to the sum of the work done in the return stroke of the compressor, i. e., the area (1 and the work temporarily stored in the buffer cylinder, i. e. the area c.

When one buffer cylinder only is employed, the energy acting from the combustion cylinder outwards, i. e., from inside upon the free-piston masses, is represented by the areas a and c. The energy acting from the outside comprises the areas b, d and. e.

The speed of a. free-piston engine in strokes per unit time depends on the one hand on the magnitude of these energies, and on the other hand on their distribution over the stroke. This latter process is illustrated in Fig, 2, in which equal accelerating. and retarding energies are circumscribed by the curves f and g. Nevertheless, different speeds are obtained owin to the difiering distribution of the accelerating energy, which can be secured for instance by altering the method of operation of the buffer cylinder. On the other hand, whenever any modification is made to the buffer energy, the length of the stroke is also influenced, as an equilibrium represented by the equality of the areas must always prevail.

In Fig. 3 is shown a bufier cylinder I, whose piston 2 is coupled to or forms part of. a free piston. In steady service the piston 2 has a stroke h between the inner and outer end positions Hi and Ha marked in chain-dotted lines. Air under pressure, for instance, is supplied to the buifer cylinder I from the pipe 3. In accordance with the tension of the spring 5, which can be altered continuously by the spindle 6 within the required limits, the pressure of the air at supply is reduced to a definite normal value by means of the regulating valve 4.

The piston 2 is loaded by this normal pressure from the inner dead centre Hi until it reaches the feed inlet 1, while in the last part of the stroke,

when the port I has been covered. energ is stored in the cylinder l by compression of the means of the spindle 5 an initial force Pi can be set in the bulier cylinder, from which develops the final force P3 at the outer dead centre. With an initiai force P2, on the other hand, the final force rises, provided the stroke is the same, to

the value P4.

Now while in the buffer cylinder shown in Fig. 3 the initial pressure of the energy accumulation can be regulated. in Fig. 5 the beginning of comaaeaoes s pression or of energy accumulation is altered. Instead of the single feed inlet 7, there are three of these provided in the buffer cylinder 8 with 1 the piston 2, namely. the inlets III, II and I2, which can be shut off from or connected to the space i by adjusting the valve l3 by means of' the handwheel H1. The space i5 can again be fed with air at a constant pressure P1 or may be in communication with the outer air. In the latter case the feed pressure of the buffer cylinder 8 in Fig. 5 would correspond to the pressure of the atmosphere;

It can be seen from Fig. 6 that compression begins at H10, or only at H11, or finally at H12, according to the position of the valve l3. Accord ingly different final forces P10, P11 and P12 result in the buffer cylinder 8, If all three ports are open, the smallest quantity of energy is accumulated, and the greatest quantity of energy if only port Ill is open.

The energy accumulating capacity of the buffer cylinder can further be changed by altering the storage volume, i. e., the volume at the outer dead centre of the piston 2. In Fig. 7 there is provided in the bufier cylinder IS an hermetically sealing piston H which can be displaced by means of the spindle i8. As in Fig, 3 the buffer cylinder it has only one port "I, through which for instance air is supplied at atmospheric pressure or at some higher pressure.

Fig. 8 gives the corresponding diagram; The initial force Pi is always the same and the beginning of the pressure increase always lies at H7. On the other hand, in the position of the piston ll shown a final force P1"! is reached, while by moving the piston l! to the right the final pressure of the Pressure increase and thus the final force can be reduced continuousl down to the value P19, when the end-position I9 is reached.

One free piston may have two or more buffer cylinders whose absorption of energy takes place in different strokes. In this case all the buifer cylinders may be of similar design, or bufier cylinders differing among themselves may be combined with the free piston.

In Fig. 9 a buffer cylinder 20 absorbing energy in the outwardstroke and a cylinder 2| absorb ing energy in the inward stroke are provided. The two cylinders are conpected through a common pressure regulating' valve 4 to a pressure pipe 3. On the other hand the feed openings 22 and 23 are at different distances from the outer dead centre Ho and from the inner dead centre Hi, In Fig. 10 the course of the forces is shown for difiering initial pressures. The fact that the left-hand piston surface of piston 2 is smaller than the right-hand surface has the result that the initial force P20 in the cylinder 20 is higher than the initial force P21 in the cylinder 25. The same is also true at a higher initial pressure, the forces P20, and p21,, for instance, presenting themselves.

By the use of at least two bufier cylinders with energy absorption in different strokes, therefore, a much more pronounced displacement of the common centre point of the working areas of the buffer cylinders, i. e., a very efiective change in the distribution of the work along the stroke, is obtained. Thu for instance the Working surface It acting outwards may be enlarged, re-

main constant, or be reduced when the two buffer and accurate regulation of the stroke frequency.

In Fig, 11 the power pistons 25 and 25a Work in the combustion cylinder 26, thecompressor pistons 2'! and 21a in the compressor cylinders 28 and 28a, and the buffer piston 29 in the bufifer cylinder 30. The free-piston 25a, 27a, which work without a buffer cylinder, is connected to the free-piston 25, 21 through the coupling linkage 15.

The compressor piston 2'! draw in scavenging and combustion air on the right-hand side through the suction branch 3! and compresses it, to deliver it through the pipe 32 with a certain excess, and through the inlet port M into the combustion cylinder 25. The compressor piston 27a draws air or gas through the suction pipe 3 la and delivers it through the delivery valves into the delivery pipe I6, which is connected to a consumption main forair or gas.

The fuel pump 55, whose plunger performs a compression stroke through the cam 18 in the inner dead center of the free-pistons, delivers fuel through the injection valve l9 into the combustion cylinder 26, The injection is adjusted by linkage ll. At the end of the expansion stroke of the free-pistons the exhaust ports 59 open and the combustion gases are led oiT by the pipe Bil. The energy of the combustion gases can be utilized in the turbine (not shown in the drawing) which drives, for instance, auxiliary equipment such. as lubricating oil pumps, cooling-water pumps and the like, or a precornpressor for the compressor 28 or for the compressor 28a. A buiier cylinder and a buiTer piston (not shown in Fig. 11) may be provided on the compressor 28a, formed like the buffer cylinder 39 and buffer piston 29 on the compressor 28, so that each freepiston is connected to one buffer cylinder only, the free-pistons 25a, Z'ia being connected to one that absorbs energy duringthe outward stroke and the free-piston 25a, 21a to one that absorbs energy during the inward stroke.

The air excess depends on whether the freepiston engine works only as a power gas producer or whether compressed air is supplied through one of the pipes branching on from the pipe 32 to other consumers. This determines the size of the compressor cylinder 28.

The left-hand side of the compressor cylinder 28 draws in air from the pipe 35 and compresses it. The compressed air is supplied through ports 3B into the pipe 37 and, in the position of the change-over member 38 shown, through the pipe 39 and the inlet port ill also to the combustion cylinder 26. A larger or smaller number of the ports 35 are closed according to the position of the piston M, which can be altered by means of the handwheel 32 and the worm gear 53. Consequently the delivery of compressed air into the pipe 3! stops as soon as the piston 2'? has covered the last open port 36 during the inward stroke. From this point on the lefthand side of the compressor 28 works as a butler cylinder with pressure increase during the inward stroke.

If the change-over member 38 is moved from the position I into the position II, the left-hand side of the compressor 28 works exclusively as a buiTer-cylinder in the sense of Figs. 5 and 6. The pipe lit can then be in communication with the outside air or may supply a gas under pressure.

The buffer cylinder fill with energy absorption in the outward stroke is fed through the pipe 45 at a pressure which is kept constant and regulated by the pressure regulating device dB. The supply M and discharge 58 of compressed air are shut oil from the pipe 45 by means of the valves 46 and 50. The valve rod 5| is provided with stops for opening the valves 49 and 56 and is loaded on tne one hand by the spring 52 and on the other by the pressure in the membrane 53 which is in communication with the pipe 45. The tension of the spring 52 is set simultaneously with the displacement of the piston 41 by means of the handwheel 42. If it is increased, the force of the spring 52 is strong enough to open the valve 49 until, owing to the entry of compressed air from the pipe 41 to the pipe 45, the loading of the valve spindle 5| by the membrane 53 balances the loading of the spring 52, Otherwise the bufler cylinder 30 works in the same way as the buffer cylinder l in Figs. 3 and 4.

In Fig. 12 the free-piston engine has two freepistons .25, 21, 29 which work with the combustion cylinders 26, the compressor cylinders 28 and the buffer cylinders 30 and 54. The stroke of the two, free-pistons 25, 21 and nised by a coupling linkage not shown in detail in the drawing but indicated by dash-dotted. lines at 15, Fig. 11. The fuel pump 55 injects fuel through the fuel valve 56 in the neighbourhood of the inner dead centre of the free pistons. The necessary combustion and scavenging air is sup- 29 can be synchroplied by the single-acting compressor cylinders 28 through the pipe 51 to the inlet ports 58. As the free-piston engine works as a power gas generator, the power gas emerges through the outlet ports 59 under pressure into the pipe 60 which leads to a power gas consumer not shown in the drawing, for instance to a turbine which drives a generator, a ships propeller or a machine doing work.

The two buffer cylinders are fed through the pipe 6|, the two buffer cylinders 54 through the pipe 62 from the container 63 as in Figs. 3 and 4. The feed pressure is regulated by means of the pressure regulating devices 64 and 65 whose design and method of working correspond to the regulating device 46 described for Fig. 11.

The normal pressure for. feeding the buffer cylinders 30 and 54 is adjusted by the lever 66 which at the same time sets the quantity of fuel to be injected by the fuel pump 55. By means of the lever 66, the rod 61 and. thus the cams 68 and 69 can be displaced, so that the loading of the springs 10 and H can be adjusted according to the profile of the cams 68, 69. By a special design of the paths of the cams 68 and 69 the change in the feed pressure of the buffer cylinders 30 and 54 can be brought into a quite definite proportion to the change in the fuel quantity to be inJected. Moreover, these cam paths can also diffen'sothflt the feed pressure for the cylinders 30 is changed in a different way from the feed pressure for the cylinders 54.

In order to be able to cut out the buffer cylinders 54 when starting up, relief valves 12 are provided. By opening these valves an increase of pressure in the cylinders 54 is prevented. It is then preferable for the connection through the pipe 62 to the tank 63 to be interrupted by clos ing the valve 13.

According to the invention it is now possible, even with two free pistons working in opposite directions, for one of the free pistons to be provided with two energy storage cylinders or buffers which absorb energy in different strokes. It is also possible, however, for one of the free pistons to be provided with a butler cylinder which absorbs energy in one stroke, for instance in the outward stroke, and for the other free piston to be provided with a second buffer cylinder whose absorption of energy takes place in the opposite stroke, that is in the inward stroke. Finally, each free piston may be provided with two or more buffer cylinders.

I claim:. 1.. Free-piston internal combustion engine which comprises at least two free pistons having at least two energy storage or buffer cylinders 2. Free-piston internal combustion engine as claimed in claim 1, which comprises a compressor cylinder having one end constructed as a bufler cylinder. 1

' 3. Free-piston internal combustion engine as claimed in claim 1, characterised inthat the piston of a. buffer cylinder is constructed to control one or more ports for feeding the cylinder with gas, preferably under pressure.

4. Free-piston internal combustion engine as claimed in claim 1, which comprises a regulating device for the feed pressure of a buffer cylinder.

5. Free-piston internal combustion engine as claimed in claim 1, which comprises a device for adjusting the beginning of the pressure increase in the buffer cylinder.

6. Free-piston internal combustion engine as 'claimed in claim 1, which comprises a device for changing the volume of the buffer cylinder.

7. Free-piston internal combustion engine as claimed in claim 1, which comprises a device regulating the feed pressure and a device for setting the beginning of pressure increase are arranged at the end of a compressor cylinder next to the combustion cylinder, in order to make possible a pressure supply during service in the first part of the stroke and in the second part the storage of energy and also, during starting, service without compression.

8. Free-piston internal combustion engine as claimed in claim 1, which comprises one or more bufier cylinders provided with a relief valve in order to enable them to be put out of action, for instance during starting. 2

9. Free-piston internal combustion engine as claimed in claim 1, which comprises a member for regulating the power of the buffer cylinders so coupled to the member regulating the power of the engine that they can be adjusted together.

HANS STEINER.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITEDSTATES PATENTS 

